Vehicle passing speed timer

ABSTRACT

A system and method for controlling an engine in a vehicle which allows the vehicle operator to manually request a vehicle speed in excess of the established vehicle speed limit that includes establishing a normal vehicle speed limit, establishing a passing duration period, establishing a passing override reset interval, and controlling the engine in response to operator input to provide a greater vehicle speed for a cumulative period not greater than the passing duration period at any time during the passing override reset interval. The system and method may include the capability of establishing a passing speed increment and controlling the vehicle speed during passing to limit the vehicle to a speed not exceeding the normal vehicle speed limit plus the passing speed increment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/430,739, filed Oct. 29, 1999 now abandoned.

TECHNICAL FIELD

This application relates to a system and method for controlling anengine to allow a vehicle operator to manually exceed an establishedmaximum vehicle speed normally imposed by the vehicle's engine controlso that the operator may safely pass other vehicles.

BACKGROUND ART

Vehicle engines, and particularly truck engines, are typicallycontrolled by electronic engine control modules which implement variousmethods of controlling the vehicle engine to optimize the operation ofthe vehicle. For example, U.S. Pat. No. 5,477,827, assigned to DetroitDiesel Corporation, also the assignee of the present invention,discloses a system and method for controlling an engine including thecapability of establishing a normal maximum speed and adding to thatmaximum speed for a selected time period as a driver performanceincentive whenever the driver operates the vehicle within certainestablished performance goals, such as minimization of idle time,selection of the optimal transmission gear, maintaining a steadythrottle, or reducing the use of engine driven accessory loads.

The capability of establishing a normal speed limit provides fleetmanagers and individual truck owners with the capability of insuringthat their truck operators drive safely and meet desired fuel efficiencyand other vehicle and engine operation goals. However, programmingelectronic engine control modules to establish vehicle speed limitswhich may, for example, maximize fuel efficiency, may otherwise limitthe operator's ability to operate the vehicle in an optimal fashion inan atypical situation, such as an emergency, or when it is desirable tosafely pass other vehicles at a speed in excess of the establishednormal speed limit for the vehicle.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide a systemand method for controlling an engine which allows the manufacturer,fleet manager, or vehicle owner to establish a normal vehicle speedlimit, but which also allows the vehicle operator to exceed thatestablished speed limit to allow the operator to safely pass othervehicles, or otherwise operate the vehicle at a higher speed in anemergency.

It is also an object of the present invention to provide a system andmethod for controlling a vehicle engine which provides the operator thecapability of manually operating the vehicle to exceed the establishednormal speed limit of the vehicle for a preselected time period,including warning the operator when the period during which the operatorcan manually override the vehicle speed limit is about to lapse.

In carrying out the above and other objects, the method of the presentinvention includes establishing a normal vehicle speed limit,establishing a passing duration period, establishing a passing overridereset interval, and controlling the engine in response to operator inputto provide a vehicle speed exceeding the normal vehicle speed limit fora cumulative passing period not greater than the passing duration periodat any time during the passing override reset interval. When implementedon an electronic engine control module, the system and method of thepresent invention thus allows an operator to override the normal vehiclespeed limit imposed, for example, by the vehicle fleet manager, for alimited period of time to allow the vehicle operator to safely passother vehicles.

In one embodiment, the method of the present invention also includesestablishing a passing speed increment. The engine is controlled toallow the operator to increase the vehicle speed beyond the normal speedlimit by an amount up to but not exceeding the passing speed increment.

In another embodiment, the method of the present invention also includesestablishing a warning period, and issuing a warning to the operatorwhenever the amount of time that the operator may manually exceed thenormal speed limit is less than the warning period. In this embodiment,the warning period is preferably set for an amount of time adequate toallow the vehicle's operator to complete his passing maneuver and returnthe vehicle to its normal speed at or below the established vehiclespeed limit.

In one embodiment, the method of the present invention includescontrolling the engine to gradually reduce the vehicle speed upon theexpiration of the passing duration period to cause the vehicle togradually slow to the normal maximum speed limit.

These and other objects, features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best mode for carrying out the invention when taken in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a system including an electroniccontrol module which may be programmed to employ the method of thepresent invention;

FIG. 2 is a flow chart generally illustrating the method of the presentinvention;

FIG. 3 is a flow chart illustrating a particular embodiment of themethod of FIG. 2;

FIG. 4 is a flow chart illustrating another particular embodiment of themethod of FIG. 2; and

FIG. 5 is a flow chart illustrating yet another particular embodiment ofthe method of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, a block diagram illustrating a system includingthe vehicle passing speed timer according to the present invention isshown. The system is particularly suited for use in a vehicle, indicatedgenerally by reference numeral 10, which includes an engine 12 coupledto a transmission 14 via a master friction clutch 16. In a preferredembodiment, engine 12 is a compression-ignition internal combustionengine, such as a four, six, eight, or more cylinder diesel engine.Transmission 14 is preferably a multiple gear ratio transmission whichis manually or semi-automatically actuated to select one of theavailable gear ratios. Master friction clutch 16 may be manually orautomatically controlled by a clutch actuator (not specificallyillustrated) as is well known in the art.

Vehicle 10 may also include various sensors 18 for generating signalsindicative of corresponding operational conditions or parameters ofengine 12, transmission 14, clutch 16, and the like. Sensors 18 are inelectrical communication with a controller 20 via input ports 22.Controller 20 preferably includes a microprocessor 24 in communicationwith various computer readable storage media 26 via data and control bus28. Computer readable storage media 26 may include any of a number ofknown devices which function as a read-only memory (ROM) 30, randomaccess memory (RAM) 32, keep-alive memory (KAM) 34, and the like. Thecomputer readable storage media may be implemented by any of a number ofknown physical devices capable of storing data representing instructionsexecutable via a computer such as controller 20. Known devices mayinclude but are not limited to PROMs, EPROMs, EEPROMs, flash memory, andthe like in addition to magnetic, optical and combination media capableof temporary or permanent data storage.

Computer readable storage media 26 include various program instructions,software, and control logic to effect control of various systems andsub-systems of vehicle 10, such as engine 12, transmission 14, and thelike. Controller 20 receives signals from sensors 18 via input ports 22and generates output signals which may be provided to various actuatorsand/or components via output ports 36. Signals may also be provided to adisplay device 40 which includes various indicators such as lights 38 tocommunicate information relative to system operation to the operator ofthe vehicle. Preferably, display 40 includes at least one illuminatedindicator such as a check engine light to alert the operator to amalfunction or error. Display 40 may also include an alphanumericportion or other suitable operator interface to provide statusinformation to a vehicle operator or technician. As such, display 40represents one or more displays or indicators which may be locatedthroughout the vehicle interior and exterior but is preferably locatedin the cab or interior of the vehicle. A data, diagnostics, andprogramming interface 42 may also be selectively connected to controller20 via a plug 44 to exchange various information therebetween. Interface42 may be used to change values within the computer readable storagemedia 26, such as configuration settings, calibration variables, controllogic and the like. Interface 42 may also be used to retrieve enginehistorical information logged as a result of diagnostic or malfunctioncodes, including information which is used to assist personnelperforming routine maintenance, or troubleshooting malfunctions, as wellas engine and vehicle operation data, including data specificallyassociated with the vehicle's passing speed timer feature of the presentinvention, which may be analyzed to evaluate vehicle operatorperformance in addition to vehicle performance.

Sensors 22 preferably include an engine speed sensor 46. Engine speedmay be detected using any of a number of known sensors which providesignals indicative of rotational speed for flywheel 18, or variousinternal engine components such as the crankshaft, camshaft, or thelike. In a preferred embodiment, engine speed is determined using atiming reference signal generated by a multi-tooth wheel coupled to thecamshaft. A clutch sensor 48 may be provided to determine the clutchslip or engagement position of master friction clutch 16. An input shaftspeed sensor 50 may be provided to determine the input speed oftransmission 14. An output shaft sensor 52 may be provided to detect therotational speed of output shaft 54. Wheel speed sensors, such as sensor56, may be used to provide an indication of the current wheel speed ofone or more vehicle wheels. Such sensors are commonly used in tractioncontrol systems (TCS) and anti-lock braking systems (ABS). Of course,one or more sensors may provide signals to various other controllerswhich are eventually communicated to controller 20 rather than beingdirectly connected via input ports 22 as illustrated in FIG. 1.

As will be appreciated by one of ordinary skill in the art, most vehicleapplications will neither require nor utilize all of the sensorsillustrated in FIG. 1. As such, it will be appreciated that the objects,features, and advantages of the present invention are independent of theparticular manner in which the selected operating parameters are sensed.

In operation, controller 20 receives signals from sensors 18 andexecutes control logic embedded in hardware and/or software to implementthe vehicle passing speed control feature of the present invention. In apreferred embodiment, controller 20 is the DDEC controller availablefrom Detroit Diesel Corporation in Detroit, Mich. Various other featuresof this controller are described in detail in U.S. Pat. Nos. 5,477,827and 5,445,128, the disclosures of which are hereby incorporated byreference in their entirety.

Referring now to FIGS. 2 through 5, flow charts illustratingrepresentative control logic 100 of a system and method according to thepresent invention are shown. As will be appreciated by one of ordinaryskill in the art, the control logic may be implemented or effected inhardware, software, or a combination of hardware and software. Thevarious functions are preferably effected by a programmedmicroprocessor, such as the DDEC controller, but may include one or morefunctions implemented by dedicated electric, electronic, and integratedcircuits. As will also be appreciated, the control logic may beimplemented using any of a number of known programming and processingtechniques or strategies and is not limited to the order or sequenceillustrated here for convenience only. For example, interrupt or eventdriven processing is typically employed in real-time controlapplications, such as control of a vehicle engine or transmission.Likewise, parallel processing or multi-tasking systems and methods maybe used to accomplish the objects, features, and advantages of thepresent invention. The present invention is independent of theparticular programming language, operating system, or processor used toimplement the control logic illustrated.

Block 102 of FIG. 2 represents initialization of various programmingvariables and thresholds, one or more of which may be determined duringinitialization or reprogramming of the system. Other values may beretrieved from a non-volatile memory or computer readable storage mediaupon engine start-up or other event such as detection of a fault orerror. The reference values are determined and stored in memory, andpreferably include vehicle speed, normal maximum speed, passingduration, and reset interval. Vehicle speed may be sensed directlyand/or derived from the gear ratio and/or one or more of sensors 18. Thegear ratio may be communicated by a transmission controller but ispreferably a virtual gear ratio (VGR) which may be determined using theratio of transmission input to output speed. One of ordinary skill inthe art will recognize a number of methods to determine transmissioninput and output speeds which may be directly sensed or indirectlyinferred from various other sensed parameters.

The passing duration and reset interval values, as well as the thresholdvalues for other operating parameters described hereinafter, aretypically programmed into the computer readable storage media 26 viainterface 42 during the initial configuration of the engine control, orsubsequently by the truck owner or fleet service personnel. Thereference values determined by block 102 are periodically reset orcaptured (and stored) based on occurrence of one or more predeterminedevents.

The normal maximum road (vehicle) speed limit is typically set by thevehicle owner or fleet manager at a value which maximizes fuelefficiency, and/or otherwise maximizes the economical operation of thevehicle.

The passing duration is the time period during which the driver isallowed to manually request vehicle speed in excess of the normalmaximum vehicle speed. In one embodiment, this time period may beprogrammed to be between 0 and 255 minutes, and is typically of about 30minutes duration. It should be noted, however, that the system of thepresent invention can be configured to accommodate a passing durationperiod of greater than 255 minutes, if so desired.

The reset interval is the period of time after which the electroniccontrol module 20 reestablishes the passing duration, to enableoperation of the vehicle at passing speed in excess of the programmedvehicle speed limit for a period of time up to the passing durationperiod during the next interval. The reset interval is preferably 24hours, but it can be any desired time period. In one embodiment, thereset interval is reestablished (i.e., a new 24 hour period begins) uponthe lapse of the previous reset interval, regardless of the real time.In an alternative embodiment, the reset interval may be reestablished atmidnight, based upon the real-time clock in the controller 20 in lieuof, or in addition to, reestablishing the interval period at the lapseof the current interval.

The threshold values for other operating parameters utilized in themethod of the present invention, such as the passing speed increment theupper activation throttle position, the lower activation throttleposition, the throttle sequence activation period, the warning period,and/or the ramp-down time are also preferably initialized at 102 asdescribed above.

As indicated at 104, if the passing speed timer is enabled, the systemperiodically determines whether the operator has made a manual speedrequest, such as by moving the foot pedal. It should be noted that it iscontemplated that the passing speed timer of the present invention willbe enabled to provide speed in excess of the vehicle speed limit to theoperator only upon manual input by the operator, since it is anticipatedthat this excess speed will be utilized only for passing or otherunanticipated emergencies. Thus, if the operator has not made a manualrequest for speed (e.g., cruise control or another automatic speedcontrol is in effect), the system exits the passing speed logic 100. Ifthe driver has made a manual speed request, the system checks, at 106 todetermine whether the requested speed is greater than the normal vehiclespeed limit. If the requested speed is within the normal vehicle speedlimit, the system exits logic 100.

In one embodiment, the passing speed adder of the present invention isactivated by a specific positioning sequence of the throttle. In thisembodiment the driver must press the throttle pedal above an upperactivation throttle position (preferably between 60 and 99% of fullthrottle, and most preferably about 95% of full throttle), then releasethe throttle to a position below the lower activation throttle position(preferably between 1 and 50% of full throttle, and most preferablyabout 5% of full throttle), then above the upper limit again, then belowthe lower limit, and then above the upper limit for a third time, allwithin a specified activation period. The activation time may be anypreselected time which is adequate to allow the driver to move thethrottle through the sequence of positions required to activate thefeature. This time period is preferably set to between 1 and 20 seconds,and most preferably about 3 seconds.

It will be appreciated that other predefined throttle positioningsequences may be utilized to activate the passing speed timer of thepresent invention. The sequence should preferably be simple, relativelyquick to perform, and preferably not a sequence of throttle positionswhich might be encountered in the course of normal driving.Alternatively, a separate switch, or other operator signaling device,may be utilized to activate the passing speed adder without departingfrom the spirit of the present invention.

It should be noted that it is contemplated that the method and system ofthe present invention will be implemented in conjunction with othersystems and methods which automatically adjust the vehicle speed limit,such as the fuel economy speed limit adder disclosed in U.S. Pat. No.5,477,827, or other speed-based incentive engine controls. When themethod of the present invention is implemented with, for example, a fueleconomy speed adder, it is contemplated that the passing speedincrements, the fuel economy incentive speed adder, and any other speedadders will be cumulatively added to the vehicle's normal speed limitwhen appropriate. Of course, if desired, a programmable optimal vehiclespeed limit may be provided to limit the cumulative total of the normalmaximum vehicle speed and any cumulative total speed adders.

If (as shown at 108) the requested speed is greater than the normalmaximum vehicle speed (and any other speed adders) within a selectedthreshold time period (preferably about 20 seconds), the system willallow the vehicle to operate at a higher speed until the speed requestedby the operator drops or until the passing duration time expires (asshown at 110). If the speed requested by the operator is now below thenormal limit (at 112), the system thereafter limits the speed to itsnormal maximum (at 111). If the vehicle speed is above the normalmaximum, the system checks to determine whether the passing durationinterval has lapsed (at 113). If not, the system continues to monitorthe vehicle speed and the amount of time left in the passing durationinterval. If the passing duration interval has lapsed (at 113) thesystem restores the speed limit to the normal maximum (plus any othervehicle speed adders supported by the system) until such time as thepassing speed timer is again activated (as determined at 104).

FIG. 3 illustrates one embodiment wherein the logic at 112 of FIG. 1includes the additional capability of providing speed in excess of thenormal vehicle speed limit up to an amount equal to an establishedpassing speed increment. The passing speed increment variable in thisembodiment would be established at 102 (in FIG. 1) as a thresholdoperating parameter at the time the system is configured, or at the timethe vehicle passing speed feature of the present invention is enabled. Apassing speed increment of between one and 20 miles per hour ispreferably allowed. More preferably, the passing speed increment is tenmiles per hour. Thus, in this embodiment, the logic at 112 determineswhether the requested speed is greater than the sum of the normalmaximum vehicle speed and the passing speed increment, at 114. If so,the system limits the vehicle speed to the sum of the maximum vehiclespeed and the passing speed increment for the duration of the request,or for the remainder of the passing duration, whichever is less. If therequested speed is not greater than the sum of the vehicle speed limitand the established passing speed increment, the system allows therequested speed, at 118 for the duration of the request, or until thepassing duration period has expired, whichever is sooner.

FIG. 4 illustrates another embodiment of the present system and methodwherein the logic of block 112 (shown in FIG. 2) also includes logic fordetermining whether the passing duration period has diminished to aperiod of time less than an established warning period (at 120). If so,the system issues a warning, at 122, either in the form of a message ona graphic display, illuminating a light, activating an alarm, or othermethod of indicating to the operator that the passing speed timer isabout to lapse and he/she will shortly be limited to the normal maximumvehicle speed. In one embodiment the system will cause the check enginelamp (CEL) to flash rapidly as a warning that the passing speed durationtime is about to lapse. The established warning period is an adequateamount of time to allow the driver to complete a typical passingmaneuver. In one embodiment this period may be set at 0-255 seconds, andis most preferably about one minute prior to the end of the passingduration.

FIG. 5 illustrates additional logic which may be included in the logicat 112 of FIG. 2 which allows speed in excess of the normal maximum, butgradually reduces the vehicle speed once the passing duration period haslapsed, in order to allow the vehicle to gradually slow to the normalmaximum speed limit. The system determines, at 124, whether the passingduration period is now equal to zero. If so, the system, at 126 allowsthe requested speed in excess of maximum (or, if the embodiment of FIG.3 is implemented, the system allows the speed up to the maximum plus anyother speed adders, plus the passing speed increment). The speed is,however, gradually reduced following expiration of the passing durationperiod, preferably at a rate adequate to slow the vehicle to the normalmaximum speed within a preselected speed reduction time interval. In oneembodiment, this ramp-down time is five seconds. The engine control can,of course, use any of a variety of methods to slow the vehicle to itsnormal maximum speed including controlling the fuel supply, and/or otherengine breaking and speed control techniques such as are disclosed inU.S. Pat. No. 5,477,827, the disclosure of which is hereby incorporatedherein.

If the passing duration period has not lapsed, the system allows speedin excess of the normal maximum as described above. As with the otherthreshold values, the ramp-down time is preferably established when theECM is calibrated, or during a subsequent programming by authorizedpersonnel, such as a fleet manager. In one embodiment, the ramp-downtime may be specified to be between 0 to 255 seconds.

It will be appreciated that the various different embodiments of FIGS.3-5 may be implemented alone or in conjunction with each other so that,for example, the system may limit requested speed to the normal maximumplus an established passing speed increment, issue a warning to thedriver when the passing duration period is less than an establishedwarning period, and/or gradually reduce the requested additional speedwhen the passing duration has lapsed.

To reduce the risk of tampering, it may be required that the time of thenext reset interval, along with the current remaining duration value beperiodically stored in memory. Whenever the system clock is changed to atime which prompts reinitialization of the reset interval, the thencurrent value of the duration interval could be maintained untilcompletion of the next reset interval. For example, assume the systemestablishes the reset interval at four hours and the passing durationinterval at 30 minutes. If the vehicle has been operated so that thereis one hour remaining in the current reset interval and there is sixminutes of passing speed duration time remaining, and the system clockis moved ahead two hours, a new four hour reset interval is initiated,but only six minutes of passing duration time is allocated for the nextfour hour interval. Thereafter the passing speed duration will bereestablished to 30 minutes at the beginning of each subsequent resetinterval. In this manner, an operator cannot easily obtain a fullpassing speed duration of 30 minutes by simply resetting the clock tothe next four hour interval.

It will also be appreciated that the system of the present invention mayrecord various data associated with the use of this feature for laterreview by the operator, fleet manager, vehicle owners, or servicepersonnel. For example, the system may record cumulative time spent in“passing speed”, cumulative distance traveled in “passing speed”, andthe time and frequency of any warnings issued. This information may bedownloaded with other engine historical information using interface 42or other known methods and apparatus.

Again, the particular order of operations illustrated is for convenienceonly. Preferably, one or more of the computations/decisions illustratedare made essentially concurrently and do not depend on the result ofother operations except where necessary as will be recognized by one ofordinary skill in the art.

Thus, the present invention provides a system and method for allowing avehicle operator the flexibility to operate his/her vehicle at a speedexceeding the normal vehicle speed limit to allow the driver to performnormal passing, and to provide additional speed in limited emergencies,while limiting this capability so as not to frustrate vehicle operationand safety goals attained by normally established vehicle speed limits.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method for controlling an engine to allow avehicle operator to obtain a vehicle passing speed in excess of thenormal vehicle speed limit, the method of comprising: establishing anormal vehicle speed limit; establishing a passing duration;establishing a passing override reset interval; controlling the enginein response to vehicle operator input to provide a vehicle speedexceeding the normal vehicle speed limit for a cumulative passing periodnot greater than the passing duration at any time during the passingoverride reset interval.
 2. The method of claim 1 further including:establishing a passing speed increment; and controlling the engine inresponse to vehicle operator input to provide a vehicle speed exceedingthe normal vehicle speed limit by an amount not greater than the passingspeed increment for a cumulative passing period not greater than thepassing duration at any time during the passing override reset interval.3. The method of claim 1 further including: establishing a warningperiod; warning the driver that the vehicle speed will be limited to thenormal vehicle speed limit at the expiration of the warning periodwhenever the difference between the passing duration and the cumulativepassing period is less than the warning period and the vehicle speedexceeds the normal vehicle speed limit.
 4. The method of claim 1 furtherincluding controlling the engine to reduce the vehicle speed from aspeed exceeding the normal vehicle speed limit to the normal vehiclespeed limit once the passing duration has lapsed.
 5. The method of claim1 further including: establishing a speed reduction interval; andincluding controlling the engine to reduce the vehicle speed during thisspeed reduction interval from a speed exceeding the normal vehicle speedlimit to the normal vehicle speed limit once the passing duration haslapsed.
 6. The method of claim 1 further including: setting thecumulative passing period to zero upon the expiration of the passingoverride reset interval.
 7. A method for controlling an engine in avehicle including an internal combustion engine in communication with anelectronic control module to allow the operator to attain a passingspeed greater than the preset vehicle speed limit, the methodcomprising: establishing a normal vehicle speed limit; establishing apassing speed increment; establishing a passing duration; establishing apassing override reset interval; controlling the engine in response tovehicle operator input to provide a vehicle speed exceeding the normalvehicle speed limit by an amount not greater than the passing speedincrement for a cumulative period not greater than the passing durationat any time during the passing override reset interval; and upon theexpiration of the passing override reset interval, resetting the passingduration and the passing override reset interval to their establishedvalues, to allow for operator requested passing speed exceeding thevehicle speed limit for the next override reset interval.
 8. The methodof claim 7 wherein the vehicle speed limit, passing speed increment,passing duration, and passing override reset interval values areestablished during calibration of the engine control module.
 9. Themethod of claim 7 wherein establishing a passing speed incrementcomprises establishing a passing speed increment variable in the memoryassociated with the electronic control module with a preselected value.10. The method of claim 7 wherein establishing a passing durationcomprises establishing a passing duration variable in the memoryassociated with the electronic control module with a preselected value.11. The method of claim 7 wherein establishing a passing override resetinterval comprises establishing a passing override reset intervalvariable in the memory associated with the electronic control modulewith a preselected value.
 12. The method of claim 1 wherein the passingoverride reset interval is reset at a selected real time, and whereinthe operator is allowed to exceed the normal vehicle speed limit by anamount not greater than the passing speed increment for a cumulativeperiod equal to the established value of the passing duration periodwhenever the real time is equal to the selected real time.
 13. Themethod of claim 12 further including: determining whether the systemclock has been changed to a time which would prompt resetting thepassing override reset interval and resetting the passing duration toits established value, and if such a change has occurred, maintainingthe current value of the duration interval rather than resetting it toits established value until completion of the next reset interval toprevent an operator from obtaining additional speed limit override timeby changing the clock.
 14. The method of claim 6 further including:resetting the passing duration to its established value upon theexpiration of the passing override reset interval.
 15. The method ofclaim 14 further including: determining whether the system clock hasbeen changed to a time which would otherwise prompt setting thecumulative passing period to zero and resetting the passing duration toits established time, and if such a change has occurred, maintaining thecumulative passing period at its current value and not resetting thepassing duration until completion of the next passing override resetinterval.
 16. In a method for controlling an engine to allow an operatorto override then normal vehicle speed limit for a cumulative passingperiod which is reestablished at a predefined reset interval, a methodof determining whether the operator has tampered with the engine controlsystem clock to obtain an additional time period for exceeding thenormal vehicle speed limit, the method including: determining whetherthe system clock has been changed to a time which would promptreinitialization of the passing period during which the operator mayoverride the vehicle speed limit and, if such a change has occurred,suspending any steps which would allocate additional capability to theoperator to exceed the normal speed limit until the completion of thenext full reset interval.
 17. In a method for controlling an enginewhich provides the operator with a particular operating capability for atime period which is reestablished at a predefined reset interval, amethod of determining whether the operator has tampered with the enginecontrol system clock to obtain an additional time period for theparticular capability, the method including: determining whether thesystem clock has been changed to a time which would promptreinitialization of the time period during which the operator mayutilize the particular capability and, if such a change has occurred,suspending any steps which would provide the capability to the operatorfor any additional time.